Which animals are seasonal breeders

Animal defensive behavior Kinesis Animal escape behavior Cooperative breeding Sexual cannibalism Cannibalism zoology Animal aggressive behavior. Recent Blogs Community portal forum. Register Don't have an account? Seasonal breeders. Edit source History Talk 0. Internalization of seasonal time. Lehman, R. Goodman, F. Karsch, G.

Jackson, S. Pathways to Pregnancy and Parturition. Sheep are seasonal breeders that enter into the breeding season during shorter photoperiods; thus, they are short-day breeders. In the mid and high latitudes of temperate regions, breeding begins in autumn, when the daylight becomes shorter.

The Mechanism behind the effects of photoperiod involves the secretion of melatonin, which stimulates GnRH release. The retina of the eye is stimulated by the presence of light. When light is abundant, an excitatory pathway is active inhibiting melatonin release. Because of genetic differences, different breeds of sheep maintain different levels of photoresponsiveness.

Melatonin is a modified amino acid secreted by the pineal gland that communicates information about environmental lighting to various parts of the body.

Melatonin has important effects on maintaining biological rhythms, and has important effects on reproductive function. Light that is exposed to the retina is first relayed to the suprachiasmatic nucleus of the hypothalamus, an area of the brain well known for coordinating biological clock signals Fibers from the hypothalamus descend to the spinal cord and project back to the pineal gland. Thus it converts signals from the sympathetic nervous system into hormonal signals Bowen.

Seasonal changes in day length have profound effects on reproduction in sheep, and melatonin is a key player in controlling such events. During the non-breeding season, the gonads become inactive, but as breed season approaches, the gonads must be rejuvenated.

Photoperiod is the most important cue to allow animals to determine what season it is. The pineal gland is able to measure day length and adjust secretion of melatonin accordingly.

In species with longer gestation times, such as sheep, the anticipation of spring must occur much earlier, and seasonal changes in the fall act as a stimulus. Short photoperiods stimulate gonadol activity. Melatonin is released during the night, so as days shorten and nights lengthen in the autumn, the duration of the nocturnal melatonin peak is increased. Conversely, after the winter solstice, the photoperiod increases and the duration of the melatonin signal falls Essential Reproduction, Seasonal breeding in sheep is a serious challenge for the industry.

It reduces the effectiveness of accelerated lambing programs, restricts integrating lambing into other farm activities, and limits access to favorable seasonal markets Notter. Potential genetic improvements are possible by selection to reduce seasonal breeding. Thyroid hormone is involved in the development and plasticity of the central nervous system To understand the action of thyroid hormone within the MBH, the ultrastructure of the median eminence was examined under SD and LD conditions using electron microscopy.

Dynamic morphological changes were observed between the GnRH nerve terminals and glial endfeet within the median eminence In SD conditions, many GnRH nerve terminals are encased by the endfeet of glial processes and do not contact the basal lamina, while many GnRH nerve terminals are in close proximity to the basal lamina under LD conditions Figure 3. It has been proposed that the nerve terminals of hypothalamic neurons are required to directly contact the pericapillary space for the secretion of the hypothalamic neurohormone from the hypothalamus into the portal capillary Morphological changes between the GnRH nerve terminals and endfeet of glial processes are observed in SD quail treated with T 3 to stimulate testicular growth Therefore, these morphological changes appear to regulate or modulate the seasonal GnRH secretion from the median eminence.

It is also interesting to note that the seasonal plasticity within the GnRH system is reported in ewes Figure 3. Neuro—glial interaction between GnRH nerve terminals and glial endfeet. Locally activated thyroid hormone within the MBH regulates neuro—glial interaction in the median eminence and these morphological changes appear to regulate or modulate seasonal GnRH secretion from the hypothalamus to portal capillary.

The illustration has been modified from that published by Yoshimura Seasonal reproduction is a rate-limiting factor for the animal procreation. The photoperiodic signaling pathway could also be a potential target that facilitates human-driven domestication process.

As discussed previously, most laboratory mice lack the enzyme activity of melatonin biosynthesis pathway 82 , 83 , 90 , In addition, occurrence of selective sweeps was found at the TSHR locus in all domestic chickens This observation suggests that the TSHR may be a domestication locus in chicken Although we still do not know the correlation with domestication, it is interesting to note that photoperiodic regulation of DIO3 is absent in Syrian hamster Thus, genes involved in the photoperiodic signaling pathway could emerge as useful targets for the domestication of wild animals.

Involvement of thyroid hormone in the regulation of seasonal reproduction has been suggested in the past several decades. Recent comparative studies clearly reveal that the local activation of thyroid hormone within the hypothalamus is a key factor in the regulation of seasonal reproduction in a number of mammalian and avian species.

It is important to note that this mechanism is also conserved in fish 93 and is universal among various vertebrate species. Presumably, the responsiveness of pathways downstream of T 3 activity e.

The switching mechanism of LD breeder and SD breeder needs to be clarified in the future studies. The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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Nature — The reciprocal switching of two thyroid hormone-activating and — inactivating enzyme genes is involved in the photoperiodic gonadal response of Japanese quail. Endocrinology —4. Reproductive seasonality maximises the chance of offspring survival by timing parturition to coincide with spring when nutritional and climate conditions are optimum for lactation and for growth of the offspring. It is important to be able to distinguish between seasonal anoestrus and pathological infertility.

Both males and females exhibit reproductive seasonality. However, the female is more strongly influenced by season. During the day, light levels are detected by the retina which sends impulses to the suprachiasmatic nucleus of the hypothalamus and then to the superior cervical ganglion.